Having a sweet taste in the mouth can be caused by diabetic ketoacidosis which is a serious condition that could mean you're on the way to diabetes or you already have diabetes.
If you have a sweet taste in the mouth that doesn't go away within a day or so you need see a doctor to get tested for diabetes.
The Excess ketones in the body causes a fruity or sweet taste in the mouth with should not be ignored because it can be a serious condition that needs checked out and treated.